By now you may have heard the report that as many as 1/4 of all the sun-like stars in the Milky Way may have Earth-like worlds. Briefly, astronomers studied 166 stars within 80 light years of Earth, and did a survey of the planets they found orbiting them. What they found is that about 1.5% of the stars have Jupiter-mass planets, 6% have Neptune-mass ones, and about 12% have planets from 3 – 10 times the Earth’s mass.

This sample isn’t complete, and they cannot detect planets smaller than 3 times the Earth’s mass. But using some statistics, they can estimate from the trend that as many as 25% of sun-like stars have earth-mass planets orbiting them!

Like mass?

Now, there’s a very important caveat here: these are planets that have the same mass as Earth, but that doesn’t mean they are very earth-like. The planets the team could find were very close to their parent stars, so they’d be very hot, and uninhabitable. But the good news is that if that trend in mass they saw is correct, the Milky Way is littered with planets the mass of the Earth! If some of them are in the habitable zone of their star… well.

So a funny thing: I was thinking about this very problem a couple of days ago, but from a different angle. How many habitable planets are there in the Milky Way? Not just earth-mass, but also orbiting their star in the so-called Goldilocks Zone, where temperatures are right for liquid water?

There’s a way to estimate it. And it involves the planet recently announced, Gliese 581g. This planet is about 3 times the Earth’s mass, and it orbits its star in the right place. We don’t know what it’s made of, if it has an atmosphere, or really very much about it at all! But given its mass and temperature, it’s potentially habitable.

The distance to the Gliese 581 system is what gets me excited: it’s 20 light years away. That’s close, compared to the vast size of our galaxy. So let’s assume Gliese 581g is the closest potentially habitable planet to us. Given that assumption, we can estimate the number of potentially habitable planets in the entire Milky Way! And the math’s not even that hard.

The not-so-hard math

Extrapolating from our one example, let’s say that habitable planets are roughly 20 light years apart in the galaxy (as we’ll see, that number can be a lot bigger or smaller, and the end result is still cool). That means there’s one star per cube 20 light years on a side:

In the drawing, each box is centered on a star, and the two stars are 20 light years apart. That means the cubes are 20 light years on a side, right? If we assume stars with livable planets are distributed throughout the galaxy like this, then there is one star per 20 x 20 x 20 = 8000 cubic light years. That’s the density of habitable planets in the galaxy.

So how many cubic light years are there in the galaxy?

A lot. Let’s say the Milky Way is a stubby cylinder 100,000 light years across, and 2500 light years thick. The equation of volume of a cylinder is

volume = π x radius of disk2 x height of disk

so

volume = π x 50,0002 x 2500 = 2 x 1013 cubic light years

Holy wow! That’s 20 trillion cubic light years!

Now we just divide the volume of the galaxy by the density of stars with planets to get

2 x 1013 / 8000 = 2,500,000,000 planets

Oh my. Yeah, let that sink in for a second. That’s 2.5 billion planets that are potentially habitable!

What does this mean?

Well, that’s a whole lot of planets! That’s what it means.

What’s cool, too, is that this number isn’t all that far off from what you can estimate using the report from yesterday. Something like 25% of the stars in the galaxy are like the Sun (that’s a rough estimate, but close enough). That’s 50 billion stars. If 25% of those have earth-mass planets, that’s about 13 billion total, about five times the number I got. I’d call that pretty close! We made a lot of guesses here, so even a factor of ten isn’t so bad. And we’re not really comparing apples to apples, either, since they were looking for earth-mass planets, and I was looking for earth-like planets.

So think about it: 2.5 billion habitable planets is roughly enough for every man, woman, and child on Earth to each have a planet. You can see why I’m not too concerned with the exact math. Even if my numbers are way off, there could be as few as hundreds of millions of planets, or as many as maybe hundreds of billions in our galaxy alone that we could live on!

Again, the point being that mathematically speaking, there may be a lot of habitable planets out there. And who knows; some may be marginally habitable and we can terraform them. And then there are moons of worlds, too… I don’t think I’m speaking too far out of school if I were to speculate that for every perfect Terra Nova out there, there might be three or four more planets we could live on with some work.

Of course, I’m ignoring how we’d get there! But that’s an engineering problem, and given enough time — oh, say, a century or two — I imagine we can overcome a lot of those issues.

If, and when, we do, there will be a lot of real estate out there to poke around in.

I can’t wait for Kepler’s results. While it’s all a fun academic exercise to run the math on the very limited data set we have, it really has incredibly large uncertianty bars at this point. I want more data!

Thankfully, we are getting better and better at finding stuff out there, so I am looking forward to those error bars shrinking.

“Of course, I’m ignoring how we’d get there! But that’s an engineering problem, and given enough time — oh, say, a century or two — I imagine we can overcome a lot of those issues. ”

Hey, pretty soon, beings on other planets will be looking up and saying, “I saw something last night that can only be a spaceship from Earth.” And the scientists on those planets, not as advanced as us, will be saying “That’s highly unlikely, there’s no planet close enough to travel here in less than thousands of years.”

The metric I use is: is the planet suitable for terrestrial life? Remember that the Earth itself was incapable of supporting modern humans until almost 500 million years ago — that is, for 8/9ths of its existence. The rest of the time there was no oxygen in the atmosphere, or not enough, or there was no ozone layer, or carbon dioxide levels were so high that humans would be unable to breath.

Then there is the problem of composition. A world where sulfur dioxide or hydrogen sulfide are part of the planet’s respiration system would kill terrestrial life off pretty quickly. The planet’s crust might have a lot of toxic compounds that, if they didn’t kill terrestrial plants, would kill animals who ate those plants. Where there is only a vanishingly small chance that an exo-world would harbor a toxic virus or other pathogen, there is a much higher likelihood that the planet would have annoying — even fatal — allergens. And how many soaps, solvents and preservatives have we invented that mimic estrogen and other hormones? It is unlikely that other worlds would have naturally occuring compounds that pose a similar risk to human health?

I love reading about exo-planets and I dream of the day when we can visit them directly. But I see no reason to get exited yet about colonizable worlds.

You derive a “density of planets per cubic lightyear”, then proceed to apply it to the entire galaxy, assuming that the density is homogenous across the entire galaxy.

Given that the star density is not homogenous across the entire galaxy, why would the planetary density be?

The old drake stuff is probably a better fit: estimate the number of potentially habitable planets per star, multiply by number of stars. I wouldn’t be surprised if there was a couple of magnitude in the error (of course, given a sample of 1 across the volume, the error bar for the probability is itself… huge)

Question: what about large moons around gas giants that are in the habitable zone? Do we know how many gas giants in other star systems are in the goldilocks-zone? Do we know anything about the odds of finding large moons (like Titan or Europa) around extra-solar gas giants? The number of habitable places in the universe could be far larger if we included these places.

Belief in the inevitability of human kind visiting distant solar systems is a matter of irrational faith. Given our behavior on the planet today, this belief is completely unfounded.

We’re destroying our ecosystem with great efficiency, we’re gobbling up finite resources as though they are endless, we’re reproducing like rabbits and cannot feed our population, we engage in perpetual war and are at risk of annihilating our entire species, etc. etc.

This James T. Kirk fantasy about exploring the galaxy is misguided and irresponsible. At our current rate of destruction, society as we know it won’t last a couple centuries – we’ll be lucky to survive this one.

Let’s keep ourselves grounded and focus on problems that we can realistically attain. Pie-in-the-sky fantasies belong in sci-fi books and movies, not science blogs.

“2.5 billion habitable planets is roughly enough for every man, woman, and child on Earth to each have a planet”

Last I checked, the world population was about 6.7 billion. So 2.5 billion habitable planets wouldn’t be enough to make one for everyone. Unless I understood you wrong and you meant that each planet would support a man, a woman and a child (3 people total per planet).

Does this math mean that programmes like BSG (where they seem to stumble accross habitable worlds fairly frequently – the 12 colonies, Kobol, New Caprica, the world with the temple, Earths mk 1 and 2) might actually be more possible that one might think?

Chris @ 7 – The idea of a Galactic Goldilocks Zone is around. I seem to recall reading a long article on it in I think it was Scientific American some years ago. It reduces the number of possible stars with habitable planets by at least an order of magnitude IIRC.

I have always had a problem with the Drake Equation, as we don’t know enough to even make an educated guess at most of the variables, allowing it to give basically any answer you want. Pessimists will get very low numbers; optimists will get very high numbers.

At least this works from an observation just to show that there are a lot of “potentially” habitable planets out there. Estimating how many are actually habitable is not something I think we could reliably do.

Anyone know if SETI has checked for signals from Gliese 581g? I wouldn’t expect anything but it seems like they would have jumped on it.

Vincent Archer (#5): As I said about ten times in the post, these numbers are supposed to be rough. I also give a decent range of numbers near the end of the post. I’m OK with people being disappointed in my math, as long as they read what I write.

TechyDad (13): I was being pretty rough, given the 2.5 billion number has big uncertainties. I almost added “… or one planet per family” and then decided it was too “Lost in Space”-ish.

I can’t wait for Kepler’s results. While it’s all a fun academic exercise to run the math on the very limited data set we have, it really has incredibly large uncertianty bars at this point. I want more data!

Yes, I hate to think where the 95% confidence limits are on the current dataset.

A world without war is a more pie in the sky fantasy then finding and visiting a more earth like planet. Also if you look into it, the world’s not as bleak as people would have you believe, and “pie in the sky fantasies” by scientists are one of the main reasons for that.

Like wise the people and money being used to fund this kind of research are only in existence due to the interest in the subject. In other words, if the money wasn’t invested in this, then I can be the first the mention that it probably wouldn’t have gone to saving the whales. It’s like asking my butcher to go solve my energy bill problems.

Why do earth-like planets need to be earth-sized? Larger planets will have slightly higher gravity, but that in no way makes it uninhabitable. Smaller planets might have issues with keeping an atmosphere, but Titan shows that it’s possible. Also, why restrict it to sun-like stars? Other stars will have a different “Goldilocks” Zone, depending on their temperature. I think you’re vastly underestimating the “potentially habitable” world count.

“The metric I use is: is the planet suitable for terrestrial life? Remember that the Earth itself was incapable of supporting modern humans until almost 500 million years ago — that is, for 8/9ths of its existence. The rest of the time there was no oxygen in the atmosphere, or not enough, or there was no ozone layer, or carbon dioxide levels were so high that humans would be unable to breath.”

Yes, but planet formation is something that occurs in clumps. Most stars in the galaxy are as old or older than the Sun, so planets around them would have had plenty of time to develop life and to alter their atmospheres to be oxygen-rich.

Nekura (23): We don’t know enough about the way planets work to know if making them bigger or smaller makes them inhabitable or not. So that’s not a safe assumption. Mind you Titan is very, very cold. Put it nearer the Sun and it wouldn’t be able to hold on to that atmosphere.

Also, Gliese 581 is a smaller, redder star than the Sun, so my math automatically includes those kinds of stars. And as I point out, this is a rough estimate; there may be hundreds of billions of planets in our galaxy. Read the last few paragraphs again.

@23. Nekura: You are completely right, but when planets are very small they usually have no plate tectonics (like Mars) and that makes it harder for them to maintain life. I’m not 100% sure why, but it was something about recycling the minerals in the planet and spreading the inner planet’s heat. I’m sure google or wikipedia will have the answer.
Planets that are too big might be gas giants (which are potentially habitable, but not for terrestrial life, though they might have suitable moons like Europa).

What I dislike about these calculations is how they focus on terrestrial life. What about so-called ‘carbon planets’? A huge planet composed of mainly carbon compounds, with an atmosphere containing a lot of carbon as well. Creatures there might eat oxygen (in the form of minerals) and breathe carbon. What about life based on something different than carbon? For instance, I like to think of computers as a simple form of silicon-based life that feeds on electricity.
And that’s only a few of the possibilities.

Now get approx. area of solar system ( I’m just going out to terrestrial planets because maybe there is a physical reason for the rocky planets being crammed in the inner solar system in terms of their formation process)

>mhmm said: A world without war is a more pie in the sky fantasy then finding and visiting a more earth like planet.

That’s a strawman argument – http://en.wikipedia.org/wiki/Strawman. I didn’t claim that we could create a world without war. I said we should “focus on problems that we can realistically attain.” You’re putting words in my mouth to your advantage.

>Also if you look into it, the world’s not as bleak as people would have you believe

Really! We’re not destroying our ecosystem? We’re not gobbling up finite resources? We’re not overpopulated and still breeding like rabbits? We not [insert stupid human behaviors here]…

How would you suggest that “I look into it” – by putting my head in the sand?

@12 Methodissed: My goodness, next you’ll tell me there is no Santa Claus or Easter Bunny and that the Earth isn’t the center of the universe.

In all seriousness, if you take the federal budget as a measure of how we feel our resources should be spent, it’s pretty clear that we spend more on trying to solve our problems than ‘pie-in-the-sky’ (e.g. Social Security, Obamacare and bailouts vs. NASA). I think it’s pretty safe to say that’s been the case for as long as humans have been around. Yet, surprisingly, the problems still exist. On the other hand, spending a tiny fraction of our precious resources on the frivolous has given us things like computers and the Internet, where we are having this discussion.

I sometimes fear we spend too much effort trying to fix the problems rather than changing the world around them so that the problems no longer exist. Pursuing the exploration of other worlds is ‘misguided and irresponsible’? On the contrary; I say it’s crucial! Ad astra!

So. Where is everyone? Nothing we do to ourselves makes me feel more pessimistic about our long-term survival chances than the lack of activity up there. 2.5 billion possible planets, Even if only one in a million were to support intelligent life that’s 2500 civilizations up there. At all stages of development. You’d think we would notice something…

the zone is really an “annulus” and I really just made an estimated formula for the area of a thin annulus. You could do a more precise calc. by subtracting the areas of two circles: one the bigger circle and one the smaller circle; but I think in end it is pretty comparable in estimating. I know for “small angles” of astronomy I always use angle = r/D for r much less than D, if angle is in radians, and that works almost as good as trig.

Question: what would it take to directly image a nearby (say, within 50 LY) extrasolar planet in any detail? I’m not talking about images that look like satellite photos, but maybe enough to do a spectral analysis, and maybe even make out some very basic surface features.

Are there any technical issues that make this possible? Would it take something more than a really, really, really big telescope?

@32. Jeff: Hmm, that sounds like a good approximation. I still prefer to do it the precise way though =) But is the width of the Zone the same for all stars, or do some stars have wider zones than others?

@12 Matt: Yeah, the rumours I’ve been hearing are that other groups that have data on the system have checked their data for it, and they don’t see it even though they should have seen it if it were there. Oh well!

I’m not getting too excited about Gliese 581g, considering there is still an argument about whether the so-called Goldilocks Planet even exists! (To wit, another team of researchers have a substantial body of observations which fail to show that it’s even there. There’s enough doubt that the Extrasolar Planets Encyclopedia still lists it as “unconfirmed.”)

People who disagree with you are not trolls. “Troll” is an adjective and all it means is people who only disagree in order to start flamewars. Reacting negatively to anyone who disagrees with you is just as narrow minded and reactionary as so-called trolls are.

Faith (belief without evidence) is a not valuable commodity, except perhaps to help insecure human egos to feel better about themselves and their future. Faith is irrational and often misguided.

When it comes to better understanding reality, we should focus on logic, reason, and the methods of science. They point to the reality that humans visiting distant solar systems is *highly* improbable. It is therefore irrational to invest precious resources that could be used to solve real-world problems.

>The first extra solar explorers will be religious fanatics while you sit in the mud on Earth being all “focused”.

Seriously? You’re predicting that religious fanatics will make extraordinary scientific advances? You must be thinking of a different planet.

This tired old argument of “Let’s fix everything here on earth before we spend any money exploring space” has been repeated countless times both here and elsewhere and is, quite frankly, getting rather annoying and only serves to disrail the conversation. Disagree, yes, but can’t ya come up with something better?

I tend to think that in order to visit distant solar systems that we’re going to have to expand beyond Earth into our own solar system. I mean that we’re going to have to get resources from other places. It can’t all come from Earth. Mind you, I’m well aware all of this would probably be hundreds of years from now.

I also like to think that striving for newer/better technology is a good way to help fix some problems here on Earth ie spinoffs and so forth. Yeah, we have lots of problems here. We can’t just throw money at putting bandaids on things and making people happy. We need innovations. What better than to study how to live in space? You have to be very self sufficient in that environment. I think we could all benefit from that here on Earth.

20 light years uh? Phil – you really need to stop messing around and get that Warp drive thing figured out; or space folding. The way I figure it, I’ve got about another 30 good years left in me before I completely fall apart, so get busy there Mister, and don’t give me that “I’m an Astronomer and not a Rocket Scientist excuse, it’s not like it’s Computer Science, now is it”.

Faith is believing in yourself in spite of all evidence to the contrary. It is what provides the psychological impetus to act against all odds and that is what you need in an explorer. So, I think that what is true at the personal level is also true at the societal level. That a society which contains those who are willing to take extreme risks based on their faith that they can succeed even when it is irrational to believe they can is a society which will reach the stars before one that is risk adverse because it believes it is “irrational” to even try.

I wouldn’t call Methodissed a troll. He has a very good point about civilization as we know it not surviving another century or two just from overpopulation, depletion of resources, and various ecosystem crashes leaving an impoverished biosphere. As a biologist/ecologist, I can say it ain’t looking pretty at the moment.

There is some hope when you look at how we’ve managed to meet some challenges (clean air legislation, accountability for some polluters, CFC regulation), but most of the times I think it’s just rearranging deck chairs on the Titanic (to use a metaphor I’ve used before). Our population is outstripping our resources and that alone is enough to call into question our continued survival as a civilization, never mind the resource wars, changing climate, and pollution levels (and resistance by political parties to doing what is needed to protect our future).

However, I do strongly disagree with his idea that we need to fix X-problems first before we tackle Y-problems. That idea has been pretty much rebutted to death by specialists in many fields (economists, scientists of all types from health specialists to rocket scientists, sociologists). It is the advances made in some unrelated fields that allow us to better tackle these down to earth issues (e.g. thanks to modern technology, some of it derived from the space race, we can preserve, ship and deliver medical and food aid to areas that would otherwise be difficult to reach or even find).

The down-to-earth improvements from “misguided and irresponsible” research are legion, and well documented because there is always some myopic politician (a redundancy, that is) standing up and yelling about how taxpayers money is being wasted on sciencey stuff (or fruit fly research, or monitoring volcanoes, or spending money on buying Alaska from the Russians, etc). Listen to those politicians and we’re on our way to what writer Andrew Leonard calls the New Barbarism in which the myopically-led country is left behind.

>uudale said: This tired old argument of “Let’s fix everything here on earth before we spend any money exploring space” has been repeated countless times both here and elsewhere and is, quite frankly, getting rather annoying and only serves to disrail the conversation.

I didn’t say we shouldn’t “spend any money exploring space” (that’s another strawman argument). I support a limited space program with a focus on real-world benefits. I’m objecting to Phil’s confident (faith-driven) assertions that humans will colonize other planets.

You’ve done nothing to rebut my initial argument. You’re just complaining that people keep disagreeing with you. If you want to add meaning to this discussion, go back to my initial post (#12) and specifically explain why my argument is incorrect, i.e., the boat is sinking – we should focus our limited resources on stopping the leaks.

as valen said, “Ask ten different scientists about the environment, population control, genetics and you’ll get ten different answers, but there’s one thing every scientist on the planet agrees on. Whether it happens in a hundred years or a thousand years or a million years, eventually our Sun will grow cold and go out. When that happens, it won’t just take us. It’ll take Marilyn Monroe and Lao-Tzu and Einstein and Morobuto and Buddy Holly and Aristophenes … and all of this … all of this was for nothing unless we go to the stars. “

37: Oli. I am assuming for this calc. today we are assuming stars similar to sun with earth-like planets in the goldilocks zone. So yes, all such G type stars like sun would be about the same size and temp. as sun so the goldilocks zone would have a thickness of I would estimate 1/2 astronomical unit around each and centered approx. at 1 AU from the stars.

Cute. I my response to you I was referencing the original poster making this argument, not you specifically.

This article was about the number of habitable planets that could exist in the galaxy, and a disagreement would be someone taking exception with BA’s math, and not involve taking the thread in a different direction. It looked like that’s what he was doing.

I apologize for my assertion that Methodissed is a troll, because he probably is not. But I would still enjoy seeing discussion get back on track about the main topic of the article. It certainly would be exciting to keep looking and actually find an Earth-like planet somewhere outside our solar system.

I think we make the mastake of assuming that a Planet has to be like Earth to have life . The late Dr Carl Sagan theroized that life on Earth is addapted to the Earths enveroment life on another Planet would be addapted to that Planets enveroment . Besides what is the defination of life form? Is it only organic? In Star Trek life forms were made of all kinds of things: rocks,energy, anti-mater, androids.. In the Transformers cartoon and movies Machines were life forms. I think we have to broden our defination of life.

47: Daniel: “As a biologist/ecologist, I can say it ain’t looking pretty at the moment.”

I’ve actually taught earth science many years, and I agree . I show the classes a pie chart of energy resources of USA/UK and it is mainly fossil fuels, and a tiny sliver of the good ones like geothermal, etc. I tell them my opinion that their young generation better figure out what to do with that pie chart because it has been that distribution as long as I can remember. And for some reason , maybe I’m getting soft or desperate in my old age, but I am more and more thinking back to my youth growing up with native Americans and their philosophy about preserving the environment for the children; I’ve been thinking about that so much in recent years that I am seriously wondering if mankind really shouldn’t just go back to an aboriginal lifestyle, that worked for millenia, maybe it’ll work again. But I obviously ain’t finding many friends on this blog with that philosophy.

I read your original post and you didn’t say a thing about limited support of space exploration. If you actually support space exploration in some fashion, however limited, than I retract what I said previously.

Sorry, didn’t mean to jump on ya, but I’ve had countless arguments with people who thought the space program was worthless and all the resources going into space exploration should be used first to solve all our problems on earth.

>Daniel J. Andrews said: However, I do strongly disagree with his idea that we need to fix X-problems first before we tackle Y-problems.

I agree that there are many Y-problems that are worthy of our attention. But Y-problems should be realistically attainable.

The notion of colonizing other planets relies on so many unfounded assumptions and wishful thinking that it’s hardly worth considering, let alone writing as though it’s a foregone conclusion, i.e., it’s truly an article of faith.

“Again, the point being that mathematically speaking, there may be a lot of habitable planets out there. And who knows; some may be marginally habitable and we can terraform them … If, and when, we do, there will be a lot of real estate out there to poke around in.”

I like the way you just assume these planets are empty. Kinda like the first settlers of North America felt the whole expanse was just theirs for the taking.

I was surprised to see Phil’s bold implication that we could be traveling to other solar systems in as little as 200 years. It doesn’t seem to work in the opposite direction. He and most others on this forum have said that aliens visiting Earth is extremely unlikely because of the distance involved. While I agree there’s no evidence of such visits, if we think we’ll be traveling to other stars soon, we should drop that argument against UFOs.

What is incredible is that there are people on this planet who are discussing the possiblity of leaving the mess we made and go live on another planet without even considering whether the people on those worlds would even want us. If we found an ‘earthlike’ world, chances are they would receive our spaceship about the same way we’d treat a UFO, so the argument about whether we should spend resources to go there or not seem silly to me. We’d do better to spend our limited resources in cleaning up the mess we made here.

Can I make an important point on spending money solving problems here on earth which _everybody_ seems to be missing.

In my experience and that of many of my friends the solutions to a large number of our problems are essentially ones of politics and organisation. If approached properly solving many of our problems would not cost money but would free up money and other resources. Indeed I find it to often be the case that throwing money at badly organised institutions actually makes their problems worse!

For example, for our US audience, how much of your money would have been saved if mortgage lending in the earlier naughties had been properly regulated?

Also it doesn’t take money to save the whales. All it takes is political will in the remaining whaling countries to ban it. This is a cultural issue, not one requiring money – i.e. politics.

I’d like to add my two cents about solving our earthly problem before going out to the skies. Have you ever imagined if Spaniards would’ve used this argument to deter Christopher Columbus from travelling to the West?

The talk of colonizing planets with a higher mass than earth reminds me of a recurring theme in science-fiction, that of “heavy-worlders,” humans who’ve lived on higher mass planets long enough that they’ve bred/evolved hugely strong bodies to cope with the extra gravity. It all sounded rather unlikely to me.

An interesting point that I hadn’t realized, though, is that surface gravity doesn’t scale with mass at all – I’m horrible with math, but I understand you could have a planet that weighed, say, 2 earth masses, and the surface gravity, depending on the planet’s density, might be as low as 1.2 or 1.3 Gs.
Considering how many of us are overweight, I think that proves most people could survive on such a world with minimal accommodations 😀

@32 Wymarc: That’s a scary idea, but given the “rare earth” school of thought, it’s entirely possible. Wouldn’t that be a sumbitch, if when we finally explored the cosmos, we found only barely-sentient or paleolithic-level intelligent critters?
In that case, it probably would be wise to just not mention our pre-spacefaring history to them at all 😛

@65 Orlando: I would argue that that’s a disheartening metaphor, considering what happened when the explorers found the New World to be quite heavily inhabited. Space exploration, with the assumption that we won’t be colonizing worlds with intelligent life (even any life, for that matter) is a whole lot LESS fraught with ethical consequences, and thus even more attractive.

As an IT worker, I can tell you that we’d never make the mistake of waiting around for our databases and files to be free of flaws before backing them up. I know it sounds odd to refer to life, or humanity, in the same terms as data, but I don’t think the comparison is that out of line.
I think we can all agree that the extinction of human life on earth, by natural or artificial means, isn’t out of the question. In fact, on the timescale of the development of other species on earth, it’s pretty much inevitable.

A more interesting measure, for me at least, would be potentially habitable planets relatively close to Earth; if there’s one within 20 LYs, we get eight within 40 LYs, twenty-seven within 60 LYs, sixty-four within 80 LYs, and a hundred and twenty-five within 100 LYs.

Mind you, if you’re looking for places to live, terriforming Venus, Mars, and even Mercury would be easier.

Sure gets tiring hearing so many people (who certainly sound like they are thoughtful and educated) continue this argument that essentially states ‘the sky is falling’ here on earth. Get a grip people.
Are we really consuming all of our natural resources, or maybe only the ones we know about? Humans have been adapting to their environment for quite some time, and I think it takes a pretty egotistical and small mind to think that we know about everything that exists on Earth.

Although, if any of you want to purchase some carbon credits I’d be happy to facilitate that sale and make you feel better about yourself. Heck, I may even throw in a bridge or two.

While “we found one potentially habitable in such and such volume, apply to entire galaxy” isn’t wrong as pure mind game, if we take “number of all exoplanets discovered, compared to that one potentially habitable”, numbers get lower.

Its all just toying with Drake’s Equation. Once Kepler data starts flowing in on the other hand…

I get rather annoyed with the argument that we’re using up all the “finite resources”. The only thing we’re using up is stored energy in the form of hydrocarbons – but the hydrogen, carbon, oxygen, nitrogen, and all the other elements that make up those hydrocarbons – as well as the iron, cobalt, silicon, germanium, rare earth elements, and so forth – do not just disappear into nothingness. Ok, so a microscopic fraction of the uranium and plutonium do in our nuclear reactors – oh, well. Our problem is not one of any resource other than *ENERGY*. And it’s not even getting a supply of it that’s a problem – it’s storage and transportation that is the issue. I can barely imagine how much energy is being radiated as a 50/60 hz hum of radio waves, or dissipated as heat in transmission inefficiencies.

Don’t give me that big about depleting limited resources. Given enough energy, we can literally build any molecule we need from the pure elements.

And it’s not like the recycling programs are doing any more than spitting in the wind. Even the most aggressive local recycling program re-uses perhaps 5% of the waste from a house-hold, other than the water used to carry said waste off. There is no such thing as waste – there’s just a mine waiting to figure out how to tap it, and what to tap it for. (what to tap it for should, ultimately, be every bloody atom in it…)

The odds of humans diffusing outward into the galaxy and those of SETI finding us are not necessarily related. Even if you have faith that humans will inevitably colonize other worlds, that says nothing about the probablility that an alien will reach our particular world at this particular moment.

Tom, what I meant in comment 61 (and I think what I said) is that if it’s at all likely we can travel to other stars, we can’t argue that it’s highly unlikely that others can travel here. Whether such others exist is another matter; we don’t have any information at all to apply to that question.

Often asked question, often repeated answer, once more – relevant yet redundant

Why we need to think seriously of exploring space beyond the solar system, and why we need to try and build a base on the moon and Mars – while not having solved terrestrial problems – is “collateral benefit”: You aim for a star in the sky, but you get ten new fruits on the ground.

You see, however rational engineers and technicians think they are, they drool over sexy babes not intelligent but ugly ladies, they eat tasty and junk food but not organic, self-farmed veggies and clean meat, and they love a good fight with a technical problem. These are ape-brain behaviors. These people are very scientific thinkers for every aspect of their trade, professional skillset, and occupation, but hardly for _every_ other aspect of their life. They just let those areas remain ape-level. Life is short, they have things to achieve.

But these good smart guys will get motivated like eager kids to make a rocket to take humans beyond Neptune. However they wont think be excited about building for a village a lab of 20 off-the-shelf PCs. How many NASA employees have donated 10 PCs personally in a bunch to a village or small community? It just does not happen. A management-of-distribution problem. This does not interest or excite them at all.

On the other hand, while they build a rocket to take humans beyond Neptune, they will invent at least a dozen serious gems of technologies that solve huge problems, on a very large scale. Activism is needed in taking the benefits of scientific breakthroughs to the masses. Cell phones are the best example of this paradigm. Google, for example, uses PhD brain clusters(above mentioned super apes) to build hardware clusters to enable you and me to get the best medicinal cures for our family, to learn any number of locally useful economic skills, to build the internet itself to run things like Twitter to do things like emergency messaging.

This is why space exploration is a good thing, and needed, before we solve the resource problems on Earth.

But that is not to say that your point is weak. In this model, it is important to prevent subversion. Which alas, must be, as human history shows.
Everything gets subverted to some degree, which is what really shocks.
Some sociopaths are always positioned to do evil things. And they always do the possible evil things. This is a mathematical fact I have not yet been able to explain fully.
Why people absolutely _need_ to be so evil and also be in places of power over so numerous other powerless or ignorant people.

So if you want to fix this broken Earth, either build a rocket or chase the snakes out of their holes. Telling from experience, building a rocket is easier, is suited for youth, and as an ape myself, I must admit, is quite enjoyable
Chasing the snakes, OTOH, takes experience, swiftness and courage. Only recommended for those who don’t need the comfort of a home.

@#75 Jamey: Technically you’re right, of course – with sufficient technology, free (ie, available) energy is the only resource you really need. But seeing as how we don’t yet have nanomachines that can comb through our waste, or fusion reactors to power our robot factories, we’re still pretty limited. Of course there’s ample energy out there (solar, etc), but it’s not cheap, concentrated energy, like fossil fuels are.

I mean, yeah, given the requisite fusion power and nanotech, we could just hollow out a comet, nudge it along at sub-light speed, and go pretty much anywhere over the course of millenia. We’re not quite there yet, tech-wise, obviously.

TechBear – Life has a nasty habit of surviving things it shouldn’t. Some toxins may be hostile to macrofauna, but that was the case on Earth at one point. This is the essence of terraforming.

Deen – What I want to know about a moon is how getting starlight blocked more than half the time changes conditions for life. Talk about a wacky day-night cycle. Bear in mind solar eclipses are rare and fleeting on Earth. On a moon, eclipses would be part of a second circadian rhythm of sorts.

Methodissed – Humans don’t move as one. While derpheads in D.C. were shoveling countless thousands of lives into a big Vietnamese meat grinder over “domino effect” ideological nonsense, scientists were launching Pioneer probes and Norman Borlaug was saving the third world from starvation. To quote Jon Stewart, I disagree with you but I’m pretty sure you’re not Hitler. If you’re more of a Norman Borlaug than Carl Sagan, though, the difference between you and Borlaug is that Borlaug actually got stuff done instead of marching all the way over to NASA to whine about whatever Sagan was doing.

Nekura – There’s a limit to star size. Red dwarfs last a long time, but the Goldilocks Zone is so close to the surface that a single flare can wipe the planet clean. More massive stars have shorter lifespans. Come to think of it:

Phil – I’ve found plenty of lifetime estimates for red dwarfs, white dwarfs, “yellow dwarfs” (read: Sol) and very short-lived stars like blue supergiants, but not much for the F-B main sequence types. (I’m talking about stars between the Sun and blue giants in mass — say, 1.5-10 solar masses? The stellar classification lines get very blurry here, given they’re more about luminosity and spectral type than mass.) Assuming the star isn’t dying, how many solar masses would you consider to be the upper limit for a star that’s likely to harbor a habitable planet?

What about an atmosphere with enough oxygen to be breathable? That seems like a requirement for a habitable planet, and I remember reading somewhere that oxygen isn’t stable in atmospheres. The only reason Earth has oxygen is because we have life that’s sustaining it, and we don’t know of any other natural mechanism that would create an oxygen-rich atmosphere. Am I misinformed?

@#76 Tome Ames: I’m reminded of Greg Egan’s “Diaspora” universe, where human consciousnesses are uploaded to orbiting supercomputers about the size of a basketball. Harvesting enough materials and solar energy to build more is trivial, so it makes a lot more sense for people to live in these virtual environments (immortal, with personal virtual surroundings unlimited by space or energy, with all the creature comforts you could possibly want) then to go planet to planet doing stuff the physical way, ie the hard way.
In that scenario, every intelligent species in the galaxy ultimate ceases to be biological. Tp physical “outsiders” like us, the only evidence that they even exist would be the occasional flashes of the gamma ray lasers they use to communicate between star systems (gamma rays having more bandwidth then radio or lasers), and those lasers are tightly aimed, so you really have to be in the right place to detect them.
An alien spacefaring race entering an “inhabited” solar system might never even notice the tiny computers in which consciousnesses dwell. It’s an interesting idea, contrary to the assumption that greater technology inevitably leads to massive energy use (ie the Kardachev scale of civilization)

Phil, I think your math is a bit off. Even assuming a homogeneous random distribution, if the nearest (whatever) is 20 light years away, there’s probably about one (whatever) on average in a cube about 40 light years on a side, not 20. That throws the density calculation off by a factor of about 8.

I don’t have the math to demonstrate this analytically, but many years ago when I was first learning to program I ran a simulation to find out how far away the nearest star is likely to be, starting with the number of stars within some number of light years. The average “closest star”, given repeated random distributions, came out close to the actual 4 light years or so. I haven’t tried the simulation lately, but Wikipedia shows 48 stars (excluding Sol) within 16.337 light-years; that’s one star on average in a cube 7.24 light-years on a side.

If each star is in a 7 or 8 light-year cube, then each cube has 6 immediate neighbors; the nearest star is the one that’s unusually close.

(If someone can manage to do this analytically rather than with a Monte Carlo method, I’d be interested in seeing the math — or at least knowing what the actual ratio is.)

>Orlando said: Have you ever imagined if Spaniards would’ve used this argument to deter Christopher Columbus from travelling to the West?

This is a faulty analogy. Spain already had the necessary technology to find an alternate trade route – they just needed someone adventurous enough to propose and try it.

In sharp contrast, colonizing other planets is a faith-based initiative, i.e., it requires huge unwarranted assumptions about our ability to fix the mess we’re currently in, survive the next few centuries, and make enormous scientific advancements.

When we have the technology to colonize other planets, then talk to me about Columbus.

As far as I can see, the case for the existence of planets f and g in the Gliese 581 system is on shaky ground. Maybe the planet d could have liquid water, maybe not. The planet GJ 1214b suggests that we might be dealing with mini-Neptunes rather than ocean worlds or terrestrial planets.

Incidentally even if Gliese 581g does exist, it is not necessarily habitable. One of the things that you tend to find if you model the interiors of super-Earth planets is that it is very likely that the cores of planets more massive than about 2-3 times the Earth’s mass are entirely solid. A solid core means no magnetic dynamo. This is not promising for habitability prospects, particularly not around red dwarf stars which experience violent flare activity for a long part of their lifetimes.

It has probably already been commented upon, but this latest epiphany about the potential for a massive abundance of “earth-like” planets in our own galaxy leads to the inevitable thought:

If there are so many earth-like planets, certainly some percentage of those (even if fairly small) must be “capable” of supporting life. And if our assumptions about the way “life” works are even remotely correct, some percentage (again, however small) of those “earth-like” “life-capable” planets must already CONTAIN life. It is then just one intuitive leap that leads to the inevitable assertion that if our assumptions about evolution, natural selection, and intelligence are even remotely correct, that some percentage of “life containing” planets likely contain “intelligent” (or at the very least, “highly evolved”) life.

Given the sheer raw numbers we are starting with, I don’t think it is all unreasonable to believe that the number of planets even in our own Milky Way galaxy that contain intelligent, or at least highly evolved life, is greater than 1 (assuming that we humans can, in fact, be considered intelligent and/or highly evolved.)

Now, on top of that, consider that fact that the Milky Way is one of an estimated 100 billion to 500 billion galaxies in the universe as we currently understand it. (That’s 500,000,000,000!)

It is arrogance of a truly massive and universal magnitude to assume that we are substantially alone in the universe.

It is, of course, also folly of an equally universal magnitude to think that we are even occasionally visited by incredibly shy and secretive extra-terrestrials (little, green, or otherwise,) that have an a fetish for mutilating cows and probing our anal cavities.

@70 AJ & @90 Methodissed: I agree with both of you. But I’m not talking about ethical consequences of exploring inhabited worlds, or technology readiness for that purpose. I think that the Age of Exploration helped to solve some old Old World problems. So, the answer for many of ours is not to hold on, but to go on, IMHO.

This is all academic. As much as the fantasy of space travel appeals, it’s just never going to happen as the energy requirements are prohibitive. Even disregarding that, then you have the issue of time scale, radiation and innumerable other massive technical problems. If our descendants ever manage to survive and move beyond earth, what will be ‘humans’ will be completely unrecognizable to us and there will never be any real inter-solar communication or galactic culture.

I wish it was otherwise, but space travel in the sense most mean will always remain the domain of science fiction. We collectively suffer from a delusion of destiny from our need to find meaning and purpose. The best we can do is hope someone invents magic.

No, he’s predicting that the religious mindset will create the will to explore when rational economics will falter.

As homo sapiens, we’re particularly ill suited for exploration, let alone colonization of anything remotely outside Earth. Sending 2 people to the Moon entailed enormous budgets, compared to sending a couple probes that yeilded more useful data for less money. All the moon exploration (the Appollo version) was nothing but faith. In the might of one country, if not in some deity.

The longer we have to go in space, the harder and more expensive it is. Barring “magical” technologies that might exist in the future. Or not.

(if you’re expecting warp drives, cryogenics, or any of those magical technologies… you’re having more faith than a lot of us)

As for colonization, assuming those magical technologies, there was a discussion on Charles Stross’ blog recently. The consensus was that, to perpetutate an early XXIst century)-level civilisation, you need to transplant about… 100 million people. Going below those margins, and you start quickly losing important, but often “invisible” elements of our civilization. Which means that the sturdy colonists are the one that care nothing about civilization, and probably are more faith-driven than most. Any “rational” person would probably look at you and scratch its head at the fact that you would want to live without most medical specialities (how many neurosurgeons has your colony?) or higher eduction for your children (how many university-level qualified teachers are your X hundred people colony be able to bring along? And if you think anyone can teach at university level , you’ve never tried to teach without having years of experience doing nothing but that).

So, yes. The faith-based efforts are far more likely to get there than any common rationalizations.

A very interesting calculation. My two cents with regard to several arguments swirling above.
Extinction of humanity: Unless we reform many of our irresponsible practices and/or wean ourselves of war we face a massive die-off. This is not to be construed with extinction. The worst atomic war one could imagine would not cause the extinction of humanity, maybe just our civilization. A new one would arise; hopefully wiser. There are seven billion of us, a few feisty hundred could repopulate.
Habitable vs. Inhabited: Billions of potential blue ocean jewels. But are they “green” — alien flora, fauna. The chemical origin of life is an open question, we have no idea what the probability is (not the same thing as evolution which is a emergent process which is a consequence of using DNA as genetic material — life could exist without DNA — cf. RNA world.) The earth is 4.5 billion years old and evidence of life exists at 3.5 billion years. The precambrian era is only 350 million years ago — the time when multicellular critters begin to dominate. Think about that. A whole long span of time with only single cells as your “advanced” species. Here’s the key point; during all that time we have evidence of only ONE chemical origin event — the one that produced the DNA biosphere and not some alternate biopolymer. NASA keeps spouting off its collective mouth that life may be everywhere; Europa, Mars, Titan. Then why are there not ten “kinds” of life here. The chemical origin of life may be very very unprobable indeed. As a corollary the lack of “alternative” life forms creeping underfoot is clear evidence we’ve never been visited by ET.

Methodissed is probably right about the likelyhood of actually colonizing other worlds. But damn I hope he/she isn’t. Faith? Naw. My faith quotient is pretty small. I call it dreaming big. Nothing wrong with that I don’t think. If I really thought that all I should do is solve all the mundane and persistant problems of life before tackling any of the really cool (in my view) problems, I might just give up and become a problem myself.

Hey realists, maybe you can work on those nasty things none of us have had much luck with over the past few millenia, and let at least some of us happily waste our time on shooting for the stars. We may not get there in our lifetimes, but I’ll guess we can come up with some pretty neat things that just might help you with your tasks while getting us a smidgen closer.

> if the nearest (whatever) is 20 light years away, there’s probably about one (whatever) on average in a cube about 40 light years on a side, not 20. That throws the density calculation off by a factor of about 8.

In this case, his math is correct. We don’t have “one earth-compatible with 20 light year emptiness on the side”, we have “2 separated by 20 light years’. Us and Gliese. If you assume that the separation is average, then yes, you’d get 1-per-8000 cubic LY average.

(which brings me to my objection that the proportion of earth-compatible should be proportional to the number of stars, not to the volume. But our esteemed host feels that getting a correct number by an incorrect method is good enough, which remembers me an old physic teacher, who, in the middle of a demonstration, paused, said “ok, 1/2 is completely negligible compared to 1”, and proceeded. But I digress)

> f there are so many earth-like planets, certainly some percentage of those (even if fairly small) must be “capable” of supporting life. And if our assumptions about the way “life” works are even remotely correct, some percentage (again, however small) of those “earth-like” “life-capable” planets must already CONTAIN life. It is then just one intuitive leap that leads to the inevitable assertion that if our assumptions about evolution, natural selection, and intelligence are even remotely correct, that some percentage of “life containing” planets likely contain “intelligent” (or at the very least, “highly evolved”) life.

And then, you fall smack on your face in front of Fermi.

When dealing with the old Drake equation, which most of us are, we have to remember that we have very little data about most of the factors. A fact which Fermi was very well aware when he was objecting to the starry-eyed optimists who were sporting large numbers of civilizations across space.

We still haven’t a good grasp on life and its evolution (while life-compatible chemistry appears easy, the evolution of local-entropy-decreasing forms of chemistry – life – isn’t that clearcut), we have even less on the development of intelligent life (as evolutionary data appears, it seems that our development of intelligence results from the confluence of a number of extremely unrelated factors, ranging from social structures, empathic models, and other sundries, all of which make the evolution of intelligent critters less and less likely), and the duration of a technic civilization (witness our problems after a mere 2 centuries of industrializationà). And those factors are as important in Drake’s equation as the proportion of earth-like worlds among stars.

There was a paper referenced on arXiv early this year (or late last year? my, time flies) that had pure statisticians putting an upper bound on civilizations in the Milky Way. Under reasonable assumptions, there’s probably AT MOST 5 civilizations in this galaxy. And the longer a civilization can function, the less there are (assuming that an average civilization lasts as long as ours did, and no more, you’d get about 20 civilizations in the galaxy)

>DTdVav Said: Methodissed is probably right about the likelyhood of actually colonizing other worlds. But damn I hope he/she isn’t. Faith? Naw. My faith quotient is pretty small. I call it dreaming big.

That’s a reasonable position – there’s nothing wrong with dreaming.

The original article and the objections that I’ve received assume just the opposite, i.e., faith in the idea that colonization is inevitable. That mindset is related to the difficulty that we as humans have in acknowledging our own mortality – of imaging a future where we don’t exist.

Some day you and I will not exist, society will not exist, and homo sapiens will not exist – probably much sooner than most people think, i.e., there are many more ways for things to go wrong than for things to go right. Though it’s possible to imagine alternate scenarios, their likelihood is extremely improbable. It is therefore most reasonable to assume the former rather than the latter.

So, dream away. When it comes to allocating precious resources, I prefer to keep our sights focused on logic, reason, and evidence.

Personally, I believe the exploration of distant planets will come through nano-tech, which should help keep costs down. In the future nano probes will do what the bulky ones do now locally and could be built for fractions of the price. Diamond nano probes anyone?

I only hope I live long enough to see life discoverd elsewhere, so the thought of 2.5 billion chances makes me happy.

My point is we can’t know what might have evolved on other plaents it can be anything .In fact it could be that if we took a life form form another planet and brought it to Earth our envoremet might kill it. This is why we need to redifine life form .I mentioned before the novel The Black Cloud by Dr Fred Hoyel The Black Clouds are large balls of hydrogen gas but they are life forms with solid brains . This is what we may find out there.As Spock says ”Its life Jim but not as we know it”

Although I think the error bars here are still huge considering how tentative this is and how many complicating factors enter the equation. (Metallicity, age of exoplanets, atmospheric factors, Galactic disasters eg. Gamma Ray bursts & supernova & passing stars disrupting comets etc ..)

One of the odd things to me is how rare Jovian and SuperJovians, heck even gas giants & gas dwarfs (which many “SuperEarths” may really be) generally, seem to be. After all :

astronomers studied 166 stars within 80 light years of Earth, and did a survey of the planets they found orbiting them. What they found is that about 1.5% of the stars have Jupiter-mass planets, 6% have Neptune-mass ones, and about 12% have planets from 3 – 10 times the Earth’s mass. This sample isn’t complete, and they cannot detect planets smaller than 3 times the Earth’s mass. But using some statistics, they can estimate from the trend that as many as 25% of sun-like stars have earth-mass planets orbiting them!

Jovians may place a big role for life evolving if they are required – as has been suggested for reducing the number of impacts by sopping up huge numbers of asteroids and comets that could otherwise impact.

Another thing that may be significant is whether it turns out the presence of a large moon like ours is needed to drive evolution from the seas via tides and just how helpful it is in other ways too.

I wonder how many worlds they might be missing, after all it is only the count so far.

I would guess the real number of exoplanets is much higher and they’ll turn out to accompany most stars based on the process of star formation which would seem to include a proplyd stage. (Protoplanetary / matter accreting disk.)

I would be surprised if there are too many stars accompanied by absolutely nothing* although I guess quite a few may have failed planetary systems with exo-asteroid and cometary belts, disks & clouds.

@ 18. rob Says:

well, if there is about one planet per person in the galaxy, within a factor of ten or so, then i call dibs on Gliese 581. i don’t want to have a very long commute.

I’m topping that by calling dibs on one of the earth-sized planets expected to be found around Alpha Centauri** and having the shortest commute of all! 😉

The closest exoplanet we know of btw. orbits Epsilon Eridani, 10.5 ly off although its a gas giant -or two – there may well be other earth-mass planets closer in.

—-

* The stars likely to have nothing are the largest mass OB spectral types like Zeta Puppis, Rigel, Achernar, Eta Carinae, Regulus, etc … They form really quickly with really short lives and extreme stellar wnds. They can also eject a lot of matter ones and their high UV may disrupt and blast away their proplyds (& even the nearby proplyds of other stars) leaving them planet-less.

** And now I’m hoping such a planet a) turns out as predicted in simulations and b) isn’t waterless or just a hostile Mars type or super hostile Venus analogue! 😉

If Phil’s guesstimate is even remotely correct, then something is wrong in the galaxy. I’d find it hard to believe that if there were over a billion worlds supporting life, no one has shown up here yet.

For the idealists and environmentalists, they have a challenge in that they look around and see only the problems. There’s a place for that but it’s all too easy to get caught up in a bleak view of where we are really at. And it’s not that bad.

The reality is that this is one of the best times in history to be alive. Seriously. There are more people living good lives now than ever before. Look at the spread of representative governments, medicine, education, and all the rest. It’s not just absolute numbers either, but also in average percentages for all of humanity.

Don’t believe me? Prior to about 1945, nearly any infection could kill you. Think about the Dark Ages when the plague was sweeping Europe and Asia. No one knew what it was (beyond bad news and death). No one had effective treatment, although they tried isolation (and nearly always failed). Their best explanation was that God was displeased and punishing them. Given their state of knowledge and circumstances, not an entirely unreasonable conclusion. At about the same time, and to add to the misery, Atilla swept in from Asia and killed thousands (millions?) more.

We have problems, yes, but we’ve always had problems. Birthrates however are falling worldwide and the population is in fact stabilizing. Whereever we fail, cruel resource limits will correct our excesses, and eventually we will learn “don’t do that because it hurts.”

All of our best achievements are because of who we are. All of our greatest failings are because of who we are. I believe we will go to the stars because some will want to badly enough. And it’s foolishness to say that it’s impossible; no one knows just how far technology can go.

As long as we don’t violate fundamental physics everything else is possible. Never forget, we still don’t even have a unified Theory of Everything. Quantum theory is incompatible with Relativity. String theory is a hopeful gleam at best and an unprovable, non-falsifiable muddle at worst. There are definite limits on what we understand about fundamental physics.

The latest thinking is that even time machines do not actually violate anything we truly know about fundamental physics. Think about that: If we can build a time machine, even if only in principle, then I think we can build an interstellar starship. I’m not sure that I’d get on board, but then I haven’t seen the ship yet either!

What is incredible is that there are people on this planet who are discussing the possiblity of leaving the mess we made and go live on another planet without even considering whether the people on those worlds would even want us.

Assuming that there will be “people” on these worlds is a huge and very likely in many (most?) cases false assumption.

Life may not be common – it may be but also may not be – and might very well mostly consist of the equivalents of bacteria and “primitive life forms.” Intelligent, technological life is probably incredibly rare based on Earth’s natural history where in 4.5 billion years existence there’s only one species like us.*

If we found an ‘earthlike’ world, chances are they would receive our spaceship about the same way we’d treat a UFO,

What they’d claim to be probed, take blurry out-of-focus images that could be of anything and become a general laughing-stock!? 😉

How would we receive a real “Flying Saucer” if it made contact in a reasonable (& clearly identifiable) way? We don’t yet know.

Probably, if they were friendly with great enthusaism and curiosity. A lot would depend on how contact happned, how well we could understand them and what they did / said to us.

so the argument about whether we should spend resources to go there or not seem silly to me. We’d do better to spend our limited resources in cleaning up the mess we made here.

It is NOT zero-Sum! We can and are very well advised to do BOTH There are plenty of people and resources on the planet to put into both “cleaning up our act here”*and also*“exploring and settling elsewhere.”

That “Either Clean up Earth or Explore Space” argument is a pure example of the “false dichotomy” logical fallacy.

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*Okay maybe also Neanderthals and Homo erectus / habilis & maybe the scientific Flores isle “hobbits” but they of course are of unknown intelligence and limited technology. How smart theywere is unclear and for the “hobbi’s whether the discovery is even real is contentious as some anthropologists argue the hobbitskelteons were just malformed, diseased adolescents of homo sapiens.

Okay maybe also Neanderthals and Homo erectus / habilis & maybe the scientific Flores isle “hobbits” but they of course are ofunknown intelligence and limited technology. How smart they were is unclear and for the “hobbits” whether the discovery is even real is contentious as some palaeontologists argue the hobbit skeletons were just malformed, diseased adolescents of Homo sapiens.

For those who forget or hadn’t heard about the “hobbit” anthropoid species see here :

The reality is that this is one of the best times in history to be alive. Seriously. There are more people living good lives now than ever before.

Spot on. I second that.

I’ll also add that Western civilisation is the greatest one ever as far as human rights, quality of life, technological achivement and in so many other ways too.

We are living in the golden age. Our way of life is the best so far possible. We have knowledge, capabilities and freedom unheard of in past generations and civilisations.

I wish more people would appreciate just how incredibly lucky we are & I really don’t understand why so many comfortable Westerners – esp. on the Left wing of politics and in the Enviromental movement are so keen to undermine and insult our Western civilisation, all too often unfairly criticising it and supporting its enemies and their ways instead.

Yes, there’s always room for improvement &, yeah, we’re not perfect but, for pity’s sake, let’s try and get things in historical and social perspective and value the good things we’ve got and the positive, sometimes arguably over-tolerant, values we hold.

@105. mike burkhart :

My point is we can’t know what might have evolved on other plaents it can be anything .In fact it could be that if we took a life form form another planet and brought it to Earth our envoremet might kill it. This is why we need to redifine life form .I mentioned before the novel The Black Cloud by Dr Fred Hoyel The Black Clouds are large balls of hydrogen gas but they are life forms with solid brains . This is what we may find out there.As Spock says ”Its life Jim but not as we know it”

book by biologist Jack Cohen and mathematician Ian Stewart which I read recently is a fascinating & very thought-provoking one on that issue. I read the “What Does a Martian Look Like?” version a few months ago & would highly recommend it even though I have to say I don’t agree with everything its authors said.

This is all academic. As much as the fantasy of space travel appeals, it’s just never going to happen as the energy requirements are prohibitive.

Yeah, that’s what they said about any space travel not too far into our past & just like humans were never going to fly, and they used to think travelling at horrific speeds like 25 miles an hour(*gasp!!*) was impossible too. Such speeds so much faster than the fastest horseman could manage would surely prove fatal to the human body which Gawd never meant to go so quickly!

So there’s no point trying to do those things or imagining what might possibly happen if we could because they’re plain impossible, rii-iight?

Break the sound barrier can’t be done!

Send a spacecraft to the Moon? Don’t be silly everyone knows rockets can’t travel in outer space because, der, there’s no air for them to push against* – and if you somehow did land on the Moon you’d just sink straight in and vanish into the pools of dust covering the entire surface! 😮

Travel around the world? [Hysterical laughter], Don’t be absurd you’ll just sail right off the edge! After all, the world is flat.

Thank the Flying Sphaghetti Monster that intelligent, imaginative, brave people throughout history (& today still) ignore those defeatist, unproductive nay-sayers like you! 😉

Even disregarding that, then you have the issue of time scale, radiation and innumerable other massive technical problems. If our descendants ever manage to survive and move beyond earth, what will be ‘humans’ will be completely unrecognizable to us and there will never be any real inter-solar communication or galactic culture.

Never say never. 😉

Are there issues to beat? Naturally.

Is it possible we’ll imagine and create and eventually take for granted ways of overcoming those issues? You betchya! 😉

If we do as you seem to wish & give up without even trying then maybe we’ll never get anywhere but you under-estimate the things human ingenuity and hard work can accomplish at your peril.

I wish it was otherwise, but space travel in the sense most mean will always remain the domain of science fiction. We collectively suffer from a delusion of destiny from our need to find meaning and purpose. The best we can do is hope someone invents magic.

Yet we have *already* invented magic!

I can go into a dark room, make a specific gesture performing a ” magic ritual”** then suddenly that room will be full of light, I can fly, I can travel vast distances in times that would formerly be considered impossible, I can see what people are doing on the other side of the planet at will. I can converse with friends when they’re not physically in the same country let alone the same room! I can play chess with magical machines that have no apparent physical form or presence. I can predict (with a little help form a “djinni in a box”***) when an artificial wandering star, a “brick moon”+, will move across the sky and like a great shamen I can foretell the times of the eclipses and need not fear them or the dreaded comets! 😉

Our technology is already magic! The things we can do and complacently take for granted every single day would get us burned at the stake as witches and wizards in medieval Europe. We are living in a world of magic and Science Fiction right now.

I’m not sure. Currently it is impossible based on our current understanding of physics although we can already imagine a few loopholes such as wormholes which serious physicists have suggested may exist.

But our understanding of physics is always changing as we learn more and theorise more.

Can we really and truly totally rule out ever getting an idea, an advance in our comprehension of the cosmos and technological capability that allows us to do this “impossible” thing?

I’d say not. 😉
—

* That’s utter tripe and totally wrong of course but many people of the time argued this. Even scientists and engineers put that error inprint and would look really foolish not too many years later.

** Called flicking the light switch!

*** a.k.a. the computer and internet.

+ Well okay this moon isn’t actually made of brick but metals and plastics – allow me some poetic lisence here please! 😉

Actually, our Sun is & has always been getting slightly hotter and brighter as it evolves and will evolve into a sub-giant overheating our planet beyond habitability in about 1.5 billion years. Then it will swell and cool ballooning out into a red giant star many times hotter and brighter again before ejecting its outer layers in a planetary nebula and leaving behind a white dwarf. The Earth will get melted down and might be totally consumed during that red giant stage. If Earth escapes – & due to the Sun losing mass & thus Earth’s orbit getting larger it may – it will be left revolving around a tiny intense pinprick of a sun, the exposed degenerate solar core now a white dwarf star. Then the white dwarf Sun will cool until eventually its light does go out leaving a dead frozen black dwarf as its ultimate stellar corpse.

So our Sun will brighten and swell and perhaps destroy us *and* then cool off, fade away and go out!

Something to look forward to eh? 😉

@ 85. Dragonchild :

I’ve found plenty of lifetime estimates for red dwarfs, white dwarfs, “yellow dwarfs” (read: Sol) and very short-lived stars like blue supergiants, but not much for the F-B main sequence types. (I’m talking about stars between the Sun and blue giants in mass — say, 1.5-10 solar masses? The stellar classification lines get very blurry here, given they’re more about luminosity and spectral type than mass.) Assuming the star isn’t dying, how many solar masses would you consider to be the upper limit for a star that’s likely to harbor a habitable planet?

Stars with masses of between 1.05 and 2 solar mass are spectral type F (Procyonese yellow-white main-sequence stars) and live between 8.8 to 1.8 billion years.

Suns with masses from 2 to 4 solar are white-hot “Sirian” A type stars and live from 1.8 billion to just 300 million years.

Stars with 4 to 20 solar masses are B type blue dwarfs and live from 300 million to only 6 million years.

I’ll also note that the more massive the star the shorter it lives & the rarer it is with A & F stars making up just 4% of all stars and O & B stars combined comprising less than 1% of the stellar population – although they’re so bright that B types particularly can be seen a-plenty in our skies.

For a star to use its hydrogen at a slow enough rate to ensure a stay of at least 3 billion years on the main sequence (to give it time to develop habitable planets) it must have a mass not more than about 1.43 times that of our Sun. This means that to have habitable planets a star cannot have a spectral class “earlier” than F2. Stars of spectral classes O, B, A, F0 and F1 cannot be expected to have habitable planets (though they may have planets). They just don’t have the time for it.

Europa has that ish in droves. It is Ice plates though. I know you probably meant plate tectonics to keep a constand stream of gasses from the innter planet out to the atmosphere. Io almost certainly does though and even as little as it is it has some atmosphere.

The stars likely to have nothing are the largest mass OB spectral types like Zeta Puppis, Rigel, Achernar, Eta Carinae, Regulus, etc … They form really quickly with really short lives and extreme stellar wnds.

Regulus is a bad example: it has a low-mass white dwarf companion star (discovered in 2008 – even bright, well-known stars can still spring surprises), and low-mass white dwarfs are produced by mass transfer. The B-type star was originally less massive and luminous until it accreted mass and angular momentum from its companion star. If you work out the likely evolution of the progenitor system, Regulus was probably originally a binary of two A-type stars and is likely around a billion years old.

Well, I can nit-pick here – somebody’s already mentioned the Galactic Goldilocks zone; I don’t need to repeat that. Though I have drafted a couple of stories on a planet that has entered the halo:
“Out here in the perimeter there are no stars
“We are as stoned immaculate …”

There’s also the meaning of “habitable” – on Earth we’ve managed to adapt ourselves to the widest variety of environments of any species – and the meaning of “human being”, because, if we get to the stage where we can adapt ourselves to new environments – Blish’s pantropy, that may open up a magnitude more planets as habitable.

So we have terraforming, and pantropy … and not forgetting the possibility of building O’Neil space colonies, and permutations without number ….

What does this do to the Fermi Paradox (roughly – where are all the extra terrestrial civilisations?) and the Drake Equation (how many detectable extraterrestrial civilisations are there?). It also probably throws the “Rare Earth hypothesis” out the window.

“…but there is no [Fermi] paradox. They are peering through their telescopes, calculating the incredible difficulty of traveling to another star, and deciding to let others, somewhere else, make the effort. That’s what I would do. ”

Perhaps this is a pie-in-the-sky point to make, but isn’t it possible we’re not approaching this “vast distances” thing objectively?
Sure, to us it seems impossible to travel even a few light years, given the time it would take. But what if there was no time limit? We’re scaling our expectations based upon our natural lifespans.
So far, nothing we’ve learned about human anatomy seems to indicate that aging itself is anything but yet another physical condition that can be treated or even “cured”. Life extension is a field that is rapidly moving out of the realm of science-fiction; in fact I’d wager that the ability to neutralize aging is achieved before the first permanent extraterrestrial settlement in our own solar system. Spending a couple hundred years or so on a spacecraft might not seem so bad if you expect to live for many millennia (barring unfortunate accidents).

This is great stuff — as speculation goes! And it’s ALWAYS fascinated me…even from a theological point of view. C.S. Lewis, great Christian thinker from the last century, had a lot to say about Space out there…. especially as it relates to the possibility of “non-fallen” creatures. Wow! Think about it: suppose we “found” a race of people — or rational creatures — sentient creatures — who had NOT fallen! Think of the implications…
And yes …. God may have indeed “created” whole populations of creatures “out there….”
Sorry, I’m not smart enough to know…
I did find some of the arguments in the “string” about the math and physics to be interesting…. and I also think that, no matter which systems one uses for the speculations, there are STILL large numbers of “potential” habitable places… Even more interesting is: what will the Creatures be LIKE? If we find them?
Right…. well, email me if u like…. thanks, R B

If Phil’s guesstimate is even remotely correct, then something is wrong in the galaxy. I’d find it hard to believe that if there were over a billion worlds supporting life, no one has shown up here yet.

That just means that the likelihood of a life supporting earth-like planet evolving an intelligent species that develops technology both capable of an interstellar journey and susceptible to detection by us, and that survives long enough to use it is something less than 1 in 10 billion.

And that, given what (admitted little) we know about life, intelligence, evolution, and technology, is actually quite reasonable.

While the problems you bring up are certainly real, the solutions to them are almost all just a simpler and easier version of the same types of technology that will be needed in building an interstellar spacecraft and keeping the crew alive and safe for the duration of the trip.

In short, if we have the tech to get there, we will have the tech to colonize it. Although the question that does arise is whether not an earth-like world will remain the idea target. With that level of super-tech, it may turn out that another type of planet ends up being the easiest and most economical to colonize.

I think (read: have faith) that the numbers are going to work out pretty close to your estimate, when we have enough data to make the calculation somewhat solid. A small fraction of those will be earthlike, of course. But if we have the means to get to them in substantial numbers, we will also have the means to terraform a good many of them.

Which means that Senate Chamber on Coruscant won’t be nearly big enough!

The Ward-Brownlee Rare Earth hypothesis is an interesting one. I think it’s basically right, but at the same time I think the authors are way too pessimistic. If complex life evolves on only one in a million habitable worlds, or one in ten million, that still makes it likely that multiple civilizations are out there.

How long a technical civilization is likely to last is a vexing question. If, as seems possible (probable to some) they are likely to use that technology to destroy themselves, the chances of survival will be enhanced if they have self-sufficient offworld outposts.

Personally, I acknowledge that the picture for civilization on our small planet looks somewhat grim at the moment, especially if you rely only on strict extrapolation of trends. But I think we will at some point find the will and the means to bend those trends in a more favorable direction.

Methodissed wrote (#12): “Belief in the inevitability of human kind visiting distant solar systems is a matter of irrational faith.”

That’s right.

“Given our behavior on the planet today, this belief is completely unfounded.”

That’s not right.

Faith in performing some physical feat is completely unfounded only if doing it would violate the laws of physics. Interstellar travel will be enormously expensive and difficult, but it is physically possible. I would not even call the hope for such things as warp drive completely unfounded. We have discovered new laws of physics in the past; we now can cross the ocean in a day and speak to almost anywhere on Earth in an instant. Five generations ago, both those abilities were fantasies. In my view, it’s irrational to think we’ve discovered all the physical laws there are.

“We’re destroying our ecosystem with great efficiency, we’re gobbling up finite resources as though they are endless, we’re reproducing like rabbits and cannot feed our population, we engage in perpetual war and are at risk of annihilating our entire species, etc. etc.”

All this is true; but not everyone behaves like this. Nor is any of these problems insoluble.

“This James T. Kirk fantasy about exploring the galaxy is misguided and irresponsible. At our current rate of destruction, society as we know it won’t last a couple centuries – we’ll be lucky to survive this one.”

It’s interesting that one core assumption of the Star Trek canon is the narrow escape of humanity from knocking itself back to permanent savagery in the 22nd century. As for exploring the galaxy, that’s a male dream just as was finding the New World in 1490 or heavier-than-air craft in 1900. I’ve read and reviewed books by two women who regard the Apollo moon missions as an adolescent distraction from real life. Missions of exploration may at times be ill-advised, but they are not inherently unwise or wasteful.

“Let’s keep ourselves grounded and focus on problems that we can realistically attain. Pie-in-the-sky fantasies belong in sci-fi books and movies, not science blogs.”

The problem with this is that there’s no universal agreement on what’s realistically attainable. Take climate change. Many today believe that doing anything about the excess CO2 we’re pumping into the atmosphere would be ruinously expensive. (Or at least they profess to believe that.) Experience with other environmental problems gives the lie to this gloomy view.

We will always have problems on Earth. We could spend every cent of every nation’s GDP on alleviating them and still not fix them all. Indeed, it’s often been the seemingly frivolous (to some) investments in exploration or pure science that have given us feasible solutions to previously intractable problems.

@Messier Tidy Upper – Regulus is a bad example: it has a low-mass white dwarf companion star (discovered in 2008 – even bright, well-known stars can still spring surprises), and low-mass white dwarfs are produced by mass transfer. The B-type star was originally less massive and luminous until it accreted mass and angular momentum from its companion star. If you work out the likely evolution of the progenitor system, Regulus was probably originally a binary of two A-type stars and is likely around a billion years old.

Okay, thanks.

I didn’t know they thought it was originally an A type binary system. If I may ask please, what’s your source for that?

I did know about the white dwarf companion – and its effect of making it a rapidly spinning distorted pumpkin-shaped star via online articles by Ken Croswell. (which I’ll link separately for y’all) However my guess there was that the binary* had originally been an even more massive blue dwarf as well as still late B-type Regulus. Regulus now has somewhere between 3 to 5 solar masses (different sources give different figures) and a spectral type of B7 V.

I guess the “Algol paradox” – where stellar interaction and matter / mass exchange affects the stars evolution and a star’s age doesn’t seem to be what it should be – strikes again. 😉

As one of the more familar, bright and at 77 or 78 light years the very nearest B type star I was using Regulus as an example of that type but you’re right I guess I could’ve found a better example. Acrux, Mimosa (Beta Crucis), Alycone (the brightest of the Plieades) or Spica maybe.

Incidentally even if Gliese 581g does exist, it is not necessarily habitable. One of the things that you tend to find if you model the interiors of super-Earth planets is that it is very likely that the cores of planets more massive than about 2-3 times the Earth’s mass are entirely solid. A solid core means no magnetic dynamo. This is not promising for habitability prospects, particularly not around red dwarf stars which experience violent flare activity for a long part of their lifetimes.

Very true & good point.

Actually with a mass of 3 to 4 x Earth’s Gliese 581g exceeds the maximum mass limit of 2.35 earth masses suggested by Stephen Dole & Isaac Asimov in their book ‘Planets For Man’ as quoted in my comment #114 above.

It seems likely to still be too large, maybe more of a gas dwarf, “hot ice” or ocean planet. We really still know far too little to domore than just speculate onthe possibility of life there.

@126. Chris Winter Says:

Phil wrote: “What does this mean?” Well, that’s a whole lot of planets! That’s what it means. I think (read: have faith) that the numbers are going to work out pretty close to your estimate, when we have enough data to make the calculation somewhat solid. A small fraction of those will be earthlike, of course. But if we have the means to get to them in substantial numbers, we will also have the means to terraform a good many of them. Which means that Senate Chamber on Coruscant won’t be nearly big enough!

Well, not all the habitable planets and sentient species were represented or included in the Old Republic & its Senate – The Hutts and Tattooine for example weren’t! 😉

Also many exoplanets may be suited for life yet not have intelligent species. Fr’ex Earth has only had humanity for a few million years(& only a few centuries technologically advanced) out of its incomprehensibly longer 4.5 *billion* year history – and for nearly half our Earth’s existence bacteria were the only living things here.

So while there may well be 2.5 billion habitable exoplanets perhaps only a very small fraction of them (10%, 1%, 0.001 %?) will turn out to host intelligent technological life forms on them.

Life, I suspect, may be reasonably common but *sentience* I feel is likely to be extremely exceedingly rare and this may at least in large part be the answer for the Fermi paradox.

@127. Chris Winter :

The Ward-Brownlee Rare Earth hypothesis is an interesting one. I think it’s basically right, but at the same time I think the authors are way too pessimistic.

I think we’ll probably find the truth lies somewhere beween the extremes of the picture presented by that ‘Rare Earth’ idea and the “life everywhere” case argued by Jack Cohen & Ian Stewart in their “Evolving the Alien /“What Does a Martian Look Like?’ book.

HI THERE PHIL !
FIRST OF ALL I WOULD LIKE TO THANK YOU FOR ALL YOU HARD WORK . ALL YOUR POSTS ARE VERY INTERESTING ! THIS IS TRULY ONE OF THE BEST SITES I HAVE EVER . I TOO WISH TO BECOME AN ASTRONAUT ONE DAY AND I HOPE THAT CONFIDENCE WONT DIE OUT . I APPRECIATE YOUR WORK .
PLEASE COULD YOU READ THE NEXT COMMENT OF MINE TOO.

COMING TO THE POINT… when you said that there are 2.5 billion planets which are likely to be habitable out there , is there any possibility of finding living organisms like us there ( humans) if the conditions are exactly the same and if all the exact nutrients are present there too ?
Are there going to be weirdish aliens out there depending on gravities ?
Why do habitable planets have to have earth size and the exact position from the parent star to have life ? Why cannot there be life on bigger planets or planets closer to the sun or far away ? I mean there could be another sort of life and other kinds of organisms living there . maybe , those organisms dont need liquid water . Instead they get adapted to gaseous or frozen water . can this happen ??Are we ever going to succeed in landing ” our humans ” on their planet or ever meeting with them ? something tells me we are way more advanced than them . Is that possible ?
I understand that you have many other posts to read but i would appreciate if you could make time for mine .
thank you
is your email id : thebadastronomer@gmail.com . i thought i saw it on the website in words .

@Messier Tidy Upper: see Rappaport, Podsiadlowski and Horev (2009) “The Past and Future History of Regulus”. As implied by the title, it also goes into what will happen when Regulus Aa runs out of hydrogen in its core and begins to expand. Regulus still has one or two more episodes of mass transfer still to come, and perhaps will eventually meet an explosive end.

>Chris Winter Said: Faith in performing some physical feat is completely unfounded only if doing it would violate the laws of physics.

You’re missing my point. Phil’s faith (belief without evidence) in planetary colonization is unfounded because it’s not evidence-based. For a science blog writer to pretend that planetary colonization is a foregone conclusion is irrational and irresponsible. Yes, it’s logical possible – it’s also highly improbable.

RE: Ecosystem destruction, overpopulation, etc.

>All this is true; but not everyone behaves like this. Nor is any of these problems insoluble.

That fact that not everyone behaves this way is irrelevant. Collectively we are destroying our future. To say that our problems are not insoluble completely misses point. We’re NOT fixing them and the efforts current underway are benign.

You’re not responding to my arguments – you’re just denying them. The Titanic is headed for an iceberg and you’re rearranging deck chairs, pretending that the iceberg really isn’t that big. The term cognitive dissonance comes to mind.

Methodissed wrote (#140): “You’re missing my point. Phil’s faith (belief without evidence) in planetary colonization is unfounded because it’s not evidence-based. For a science blog writer to pretend that planetary colonization is a foregone conclusion is irrational and irresponsible. Yes, it’s logical possible – it’s also highly improbable.”

Faith, as you note, is belief without supporting evidence. By definition. Why then do you condemn it for not being evidence-based?

Also, I have to wonder what sort of evidence for the likelihood of humans making homes on other planets you would accept. Humans have already lived repeatedly (however briefly) on an airless world. They have maintained bases in Antarctica for over half a century. Setting up on Mars (for example) is merely a more challenging problem in logistics.

“That fact that not everyone behaves this way is irrelevant. Collectively we are destroying our future. To say that our problems are not insoluble completely misses point. We’re NOT fixing them and the efforts current underway are benign.”

I would rather state it this way: We are at this period in history allowing certain governments of major nations to follow a path that, if continued, presents a grave risk to the future survival of civilization.

It does not follow that we, collectively, will continue to follow this destructive path. One bit of evidence: Glenn Beck’s rally back in August drew an estimated 87,000; the attendance estimate for yesterday’s Rally to Restore Sanity is 215,000.

“You’re not responding to my arguments – you’re just denying them. The Titanic is headed for an iceberg and you’re rearranging deck chairs, pretending that the iceberg really isn’t that big. The term cognitive dissonance comes to mind.”

@Messier Tidy Upper: see Rappaport, Podsiadlowski and Horev (2009) “The Past and Future History of Regulus”. As implied by the title, it also goes into what will happen when Regulus Aa runs out of hydrogen in its core and begins to expand. Regulus still has one or two more episodes of mass transfer still to come, and perhaps will eventually meet an explosive end.

Cheers for that.

Future history eh? Sounds, to me, like they’ve been reading their Asimov ! 😉

Also sounds like Regulus could be a type Ia supernova eventually – neat!

@136. Rithu Says:

is there any possibility of finding living organisms like us there ( humans) if the conditions are exactly the same and if all the exact nutrients are present there too?

Living organisms – well it seems very likely.

Like us humans? Very likely NOT based on the history of our planet where humans and humanoid creatures (Eg. Gorillas, Neanderthals, Orang utangs) are rare and recent in the fossil record.

Although there is an argument for convergent evolution making things that look like us because they serve the same biological function .. so we don’t really know.

This is all speculation & we need a *lot* more data but it seems unlikely that evolution would produce anything like us again if it was rerun.

Are there going to be weirdish aliens out there depending on gravities?

Who knows? Until we actually go exploring other planets we won’t be able to tell for sure but it does seem most probable.

Why do habitable planets have to have earth size and the exact position from the parent star to have life ? Why cannot there be life on bigger planets or planets closer to the sun or far away?

Well thekind of life we are familiar with can only cope with temperatres and otherconditions in acertain range. If it gets toohot or toocold life (our kind) cannot survive. Other kinds of life? Well we don’t know. If youread Science Fiction -or indeed the commesbt onthis and other blogs ypou’;ll encounter arange of hypothetcial alien life forms that can live on or rather inside gas giants, Venus, Titan, Europa, Pluto and even alone in deep space or on thesurfaces of pulsars so there are possibilities although whether any of these imagined creatures can reallyexist we’ll only know by searching for them – or first contact by them!

Are we ever going to succeed in landing ” our humans ” on their planet or ever meeting with them? Something tells me we are way more advanced than them . Is that possible?

Possible? Well I wouldn’t rule it out – not going to happen tomorrow or even in our lifetimes probably but you never know. 😉

Well the kind of life we are familiar with can only cope with temperatures, pressures and other conditions in a certain range. If it gets too hot or too cold, toopressurised or not pressurised enough life (our kind) cannot survive.

Other kinds of life? Well we don’t know. If you read Science Fiction – or indeed the comments on this and other blogs you’ll encounter a range of hypothetical alien life forms that can live on or rather inside gas giants, Venus, Titan, Europa, Pluto and even alone in deep space or on the surfaces of pulsars – so there *are* hypothetical speculative possibilities.

Whether any of these imagined creatures exist in reality we’ll only know by searching for them – or first contact by them! At the moment the verdict has to be “insufficent data”, we just don’t know yet but we’re working on it.

That “Either Clean up Earth or Explore Space” argument is a pure example of the “false dichotomy” logical fallacy.

One thing that I find infuriating is how this argument is so often applied to space travel and yet not other things. You can make the exact same fallacious “Don’t spend money on X until everything on the planet is fixed” ‘argument’ ( ) for funding sport, the arts, entertainment & most of the areas in life that give people pleasure and interest.

Why is it always space exploration & science generally that’s unfairly singled out here rather than say fuunding the opera or playing football etc ..

Besides – as somebody else up thread noted – we’ll *never* fix all the problems here anyhow. It can’t be done. Our “dirty” planet & general global situation will never be perfect in the eyes of all these eco-socio-perfectionists whatever we do. It is unrealistic to think otherwise. Human life is always messy and problematic, the poor will always be with us and also wars, etc ..

However much money you throw at things we’ll never get an ideal Utopia.

Although we can and are generally made better off by reasonably trying to improve things & get closer to Utopias anyhow, we shouldn’t just forget that harsh reality.

Don’t forget this is just our Milky Way galaxy that is being discussed- there are billions of other galaxies in the universe. I think it stands to reason that if the vast interstellar distances can be conquered (by whatever civilisation) then inter-galactic distances would follow soon after.

I think it stands to reason that a civilization which can invent interstellar travel (presumably having cracked the FTL problem) can also colonize/terraform pretty much anything, including large moons such as Titan: one would imagine that initial efforts would be subterranean (subtitanian?) because it’s cheaper than building a radiation shield around the whole moon (gas giants are typically not healthy things to be close to); this being said, one can also hypothesize that interstellar travel will be seen as a necessity: whereas the get-off-Earth-now crowd are worried about the Earth being hit by, say, a Mars-sized asteroid and generating an extra moon shortly after melting, subsequent generations will be more worried about things like the Sun going nova. In any event, it’ll be fascinating for the human race a million or so years down the line to look back at these comments (yes, I’m fairly sure they’ll be archived somewhere) and compare reality to the dreams of the as-yet-uninitiated members of the 21st century, ancient human race.

>>“You’re not responding to my arguments – you’re just denying them. The Titanic is headed for an iceberg and you’re rearranging deck chairs, pretending that the iceberg really isn’t that big. The term cognitive dissonance comes to mind.”

>OK, have it your way. We’re all doomed! Doomed, I tells ya!

Chris brings up a good point. If the only alternative to a far-fetched argument is annihilation then you should choose the far-fetched argument, because it is irrational to choose any path in which destruction is guaranteed. This point was well-articulated by Lincoln Cannon in The New God Argument:

“Consider, for example, the attitude we should take if we were to discover that a large asteroid is headed directly at Earth and will destroy all life on the planet when it hits us in five years. While some of us may languish in despair and others may passively await a chance or supernatural remedy, most of would naturally take up the faith position and begin planning for and building a means of destroying or displacing the asteroid, even while feeling anxious or simultaneously hoping for a lucky break or supernatural assistance.”
(http://lincoln.metacannon.net/2008_08_01_archive.html)

His definition of faith is a little different though. It is not defined as an irrational belief the unprovable. It’s more like putting one’s trust in posthumanity rather than human extinction. Either alternative is possible, but acceptance of our inevitable doom is irrational, so we should trust in and work towards posthumanity.

I think by the time we’re able to haul enough raw materials to a star to start a colony, we’ll have the technology to inhabit worlds we wouldn’t consider “habitable” today. Having oxygen in the atmosphere, or even having an atmosphere at all, may not be important to colonists with access to space suits and hydroponics.

Thanks for all the dreamers and the educated and even the occasional troll to fire people up. What a great conversation. Look at how the computer has brought people from around the world so close using this medium. No doubt we will be able to bring the stars to us some day. Some of the people in this conversation are absolute geniuses. I hope whomever figures it all out still has some spirituality left, otherwise we might as well send a computer (or silicon life form that feeds on electricity as somebody so eloquently put it). Keep reaching for the stars!!!

More calculations for you: Humans on earth have entered the technological age less than 100 years ago. Our sun has several billions years remaining. Now making the assumption that on all these planets there is just one with intelligent life it is 50-50 that its civilization is at least 500,000,000 years more advanced than ours.

Getting on one of these planets is not just an engineering problem. It’s also a physics problem. If the closest planet that’s Earth-like is, let’s say 10 light years from here, it would take 10 years to get there on the velocity of light. But then we would have relativity problems, since the time would pass as 10 years for the crew in the ship, but it would be an infinite time for us here, so we’d never be able to get feedback from the ship. Besides, you can never reach the speed of light, and nothing guarantees that the human body would survive at such high speed or acceleration to get to a speed so high in a human lifetime, and that’s also not an engineering problem. It would also require a lot of energy to get a ship to speeds as high as a decent fraction of the speed of light, more energy than we can get from the resources in the Earth, and that’s only part of a big engineering problem. And all that are just a few reasons why it’s impossible to get there. At the very least, to get to one of these planets, we would have to change many laws of physics, that are supposed to be unbreakable. That doesn’t mean someone can’t come up with a theory that contradicts Einstein and prove that theory is right, making it basically an engineering problem.

9. Chris Says:
October 29th, 2010 at 7:50 am
Isn’t there a Goldilocks zone for the galaxy as well? If you get too close to the center there is way too much radiation and too far out less heavy elements to make rocky planets.

Due to the existence of the Galactic Goldilocks Zone, this calculation is therefore a rough calculation. I recommend limiting the cylindrical volume of the galaxy into a torus that is encompassed by the Galactic Goldilocks Zone.

I agree however if there are identical planets like earth life could be either primitive or way more advanced Cuz there are other factors for evolution and progress
The probability of another earth planet is like finding another human with the exact DNA.

It is a vast, vast space and with our puny brains we are not able to comprehend the space we need to cover for travel to even one of these closest planets. Not that it is not possible, but at least not in our lifetime and the lifetimes of a few generations ahead.

Consider these: Energy for travel that long, conditions for human habitat for traveling, human mutation factors, supplies, technology (which we already know is not even passed its infancy), radiation containment and many, many other factors, which we still don’t account for.

Under all these factors we might as well think about propelling a whole planet (say Earth) — attaching a pretty good engine to it and travel with our resources till we run out (which may happen pretty quickly).